David Cameron will seek to rejuvenate one of Margaret Thatcher's main legacies when he declares that two million social tenants could buy their properties with a discount of up to £75,000.

The prime minister, who believes that discounts became "virtually meaningless" over the past decade after they failed to keep pace with property prices, will pledge to give tenants a chance to secure a "vital rung on the property ladder".

Cameron's remarks will be made at the formal launch of what is being dubbed the reinvigorated right-to-buy scheme, designed to breathe new life into one of Thatcher's most significant achievements.

The government says two million social homes have been bought by their occupants since the scheme's introduction in 1980. But numbers have tailed off to fewer than 4,000 sales last year.

Cameron will say: "I want many more people to achieve the dream of home ownership. In the 80s, right to buy helped millions of people living in council housing to achieve their aspiration of owning their own home.

"It gave something back to families who worked hard, paid their rent and played by the rules. It allowed them to do up their home, change their front door, improve their garden – without getting permission from the council. It gave people a sense of pride and ownership not just in their home, but in their street and neighbourhood, helping to build strong families and stable mixed communities.

"But, over time, the discounts were cut; they didn't keep pace with rises in property prices and this vital rung on the property ladder was all but removed. This government is now putting it back by dramatically increasing the discount rates so that we support the dreams of those council tenants who to want to own the roof over their head."

The £75,000 discount represents a quadrupling of the discount cap in London and a trebling in most parts of Britain. The average right-to-buy discount fell from 50% of the value of a property in 1998-99 to 24% in 2008-09. In London, it fell from 53% to 10%.